Electrolytic process for the manufacture of metal alkyls



March 5, 1968 K. ZIEGLER ET AL 3,372,097

ELECTROLYTIC PROCESS FOR THE MANUFACTURE OF METAL ALKYLS Filed June 28, 1965 INI @Wig

ATTORN YS.

NIN

United States Patent O ELECTROLYTIC PROCESS FOR THE MANU- FACTURE OF METAL ALKYLS Karl Ziegler, Kaiser-Wilhelm-Platz 1, Mulheim (Ruhr),

Germany, and Herbert Lehmkuhl, Mulheim (Ruhr), Germany; said Lehmkuhl assigner to said Ziegler Filed .lune 28, 1963, Ser. No. 291,562

21 Claims. (Cl. 204--59) The electrolytic manufacture of metal alkyl and especially the manufacture of lead tetraalkyl is the subject of numerous processes of the applicant, which are based upon the principle of electrolyzing a complex organometallic electrolyte, especially alkali aluminum complex compounds, between an anode of the metal whose alkyls are to be produced and a metal cathode. The anode metal dissolves with the formation of the corresponding metal alkyl, while alkali metal can be precipitated as the cathode reaction product. Operation with a mercury cathode has proven particularly advantageous, and this is described in application Ser. No. 27,220', filed May 5, 1960, now abandoned, and application Ser. No. 129,009, iled Aug. 3, 1961 (Patent 3,164,538, Jan. 5, 1965). A process employing the mercury cathode for the manufacture of tetraethyl lead which uses a mixture of potassium aluminum organic complex compounds is described in the said application Ser. No. 129,009.

The process of Ser. No. 129,009 and other previously described electrolytic processes for the production of tetraethyl lead operate in such a manner that, in each case, only one alkyl radical per mol of the aluminum organic complex is bound to the anode metal. The equivalent amount of alkali metal is precipitated at the cathode, in the form of the corresponding amalgam when workin g with a mercury cathode. The remanent radical of the complex electrolyte compound remains in the electrolysis cell as a decomposition product. This product is the free aluminum compound AlX3, in which the nature of the radicals X depends upon the complex electrolyte compound selected. In general, at least two of these X radicals are alkyl radicals, while the third can be an alkoxy radical, for example, or fluorine, or even a third alkyl radical. This free aluminum compound produced as a decomposition product of the electrolyte mixes with the metal alkyl formed at the anode, especially with the tetraethyl lead, normally, unless special precautions are taken to prevent this. It can then be withdrawn from. the electrolysis cell together with the tetraethyl lead, and the separation of these two components can be performed outside of the cell. In the above-mentioned process of Ser. No. 129,009, in which the potassium aluminum tetraethyl complex KAl(C2H5)4 is decomposed at a lead anode and a mercury cathode with the formation of lead tetraethyl and potassium amalgam, the development of the free triethyl aluminum can be prevented by adding the 1:1 complex KF-AlR3 to the electrolyte. The free triethyl aluminum produced as a decomposition product of the electrolyte is then bound to this 1:1 complex compound with the formation of the corresponding 1:2 complex compound, so that only the tetraethyl lead is produced uncombined with other reaction products.

The present invention relates to a new process for the manufacture of alkyl, for example lower alkyl containing up to 6 or 2-6- carbon atoms, and especially ethyl compounds of the metals lead, mercury, tin and antimony, preferably the manufacture of tetraethyl lead. In this process, the complex compound KAl(C2H5)4 can be likewise electrolytically decomposed at an anode of the metal whose ethyl compound is to be produced, e.g., a lead anode, and a mercury cathode, with the formation of tetraethyl lead and potassium amalgam, for example. In contrast to all the processes hitherto proposed for the electrolytic manufacture of ethyl metal, however, all the ethyl radicals of this complex electrolyte compound are utilized for the formation of the ethyl metal, not just one of them, as thas hitherto been the case in the above-mentioned process of Ser. No. 129,009. The process of the invention can be expressed in the case of the lead tetraethyl, for example, by the sum formula:

While all previously known, industrially usable processes in this eld have been based on the equation:

Accordingly, the invention provides a process for the manufacture of the ethyl compounds of the metals lead, mercury, tin and antimony, especially tetraethyl lead, by the electrolysis of potassium aluminum organic complex compounds at -an anode of the metal whose ethyl compound is to be produced, and a mercury cathode, with the formation of the ethyl metal as the anodic reaction product, which is characterized by the fact that the compound KAl(C2H5)4 is electrolyzed with the additional segregation of metallic aluminum in the cathode material, until it has been completely dissociated, according to reaction Equation I, for example.

Thus, the invention provides a process which comprises passing an electrolysis current between a cathode and an anode through an electrolyte consisting essentially of a complex of the formula KAlR4 wherein R is alkyl, the anode is a metal which can be designated Me and is lead, mercury, tin, or antimony, and the cathode is mercury. The electrolysis causes decomposition of the electrolyte according to the following equation K AlRg-l-mMe-aK-i-Al-f-mMeRn (IA) wherein R and Me are as is defined above, n is the valence of Me and the product of mf and n is 4. The metal alkyl is produced at the anode and the potassium is produced at the cathode and forms an amalgam with the mercury. The aluminum metal is present in the amalgam.

With respect to the valence of the metals, the valence states referred to are, for lead and tin 4, for mercury 2, and for antimony 3.

The basis for this new procedure lies in the following: It has developed that the amalgams of potassium and sodium behave differently towards triethyl aluminum. Sodium amalgam does not act on triethyl aluminum, even up to high sodium concentrations, and therefore the triethyl aluminum can be effectively protected against attack by sodium by separating the latter upon its formation at the cathode with mercury. If, however, an adequate possibility of contact between potassium amalgam and free triethyl aluminum is created, this triethyl aluminum rapidly decomposes according to the following equation:

In other words, out of 4 parts of the free triethyl aluminum compound, 3 parts of the complex potassiumaluminum tetraethyl compound are reconstituted. At the same time, a metallic aluminum is produced. This aluminum is separated by going into the mercury in nely divided form. Up to a fairly high aluminum content, this suspension behaves like a solution; the aluminum, however, is not genuinely dissolved, and, when suction filtered through a glass frit, it is separated from the mercury except for some amount of adherent mercury. Nevertheless, the owing characteristics of this aluminous mercury are not affected in the least. If potassium amalgam is contacted with complexly bound triethyl aluminum, such as triethyl aluminum bound to potassium fluoride or even to other electron donors (ethers, such as tetrahydrofuran,

, 3 or dialkylethers or amines), this reconstitution of potassium aluminum tetraethyl does not take place.

The aluminum suspended in the mercury does not attack tetraethyl lead in the least. Thus, it is also possible to remove the aluminum triethyl from a mixture of the latter and tetraethyl lead by means of potassium amalgam by transforming it with potassium amalgam to potassium aluminum tetraethyl, with a corresponding loss of aluminum; the potassium aluminum tetraethyl is insoluble in tetraethyl lead and so it separates on the basis of spontaneous dissociation.

The possibility is created by this novel reaction to manufacture tetraethyl lead electrolytically at a lead anode using pure molten tetraethyl potassium aluminum as the electrolyte. Care is taken only to see that a sufficient contact is assured between the reaction products primarily developing at the anode and the potassium amalgam created at the cathode. Such adequate contact can be assured, for example, by moving the electrolyte about within the cell. In like manner, however, the amalgam cathode can be moved about in the electrolyte, for example. An example of this is a rotating disc cathode which is wetted with the amalgam and immersed in an excess of the amalgam, so that a fresh mercury surface is always being exposed to the electrolysis. Here, too, a rapid reaction of the potassium amalgam with the primarily produced triethyl aluminum is assured, with the reconstitution of the complex tetraethyl potassium aluminum compound subjected to the electrolysis. It has even developed that, on a smaller scale, even without rotating discs, the time of contact between the potassium amalgam iirst formed and the mixture of tetraethyl lead and triethyl aluminum that first separates is entirely suflicient to cause the triethyl aluminum to vanish. The complex electrolyte compound reconstituted in this reaction is constantly dissociated electrolytically with the formation of tetraethyl lead. Finally, the tetraethyl lead remains in the electrolysis cell as the only component of the non-complex-ly bound liquid phase. The electrolyte, which according to the invention does not have to be a mixture but may be a single substance, is consumed in precise equivalence to the product that is formed. In the continuous electrolysis process, it is preferably fed to the electrolysis cell in corresponding amounts.

The new procedure for the electrolytic manufacture of tetraethyl lead offers considerable advantages. The cell merely requires supplementation of the electrolyte, like any other electrolysis cell. The circulation of inert auxiliary agents which has always been necessary hitherto is eliminated. The conductivity of the molten tetraethyl potassium aluminum is the highest of all the previously observed conductivities of similar substances. At 120 to 130 C., it approaches the value of 1 l01 and, in practical operation, may probably amount to at least 8X10-2. T etraethyl potassium aluminum has a low melting point (at about 70 C.), so that the requirement of a liquid electrolyte is ideally fulfilled. The hitherto ever-present problem of eliminating a dissolved remainder of tetraethyl lead from the electrolyte no longer occurs, because the electrolyte is completely consumed in the electrolysis, and furthermore the soubility of the tetraethyl lead in potassium aluminum tetraethyl is slight, anyway. So it is of no importance at all whether a little tetraethyl lead is constantly in the cell, dissolved in the electrolyte. Furthermore, as already stated, the aluminum suspended in solid form in the mercury does not in any way -lessen the mobility of the amalgam. It is possible, for example, up to a practical limit of 0.6% potassium, to add the equavalent amount of aluminum (approximately 0.4%) without producing any change in the consistency of the potassium amalgam. So there are practically no restrictions on the charging of the mercury with the metallic electrolysis products in the actual practice of the method.

In addition to all these advantages which result from the fact of the complete dissociation of the complex electrolyte compound, the process of the invention also represents a very important additional innovation. For in the continuous electrolysis process, it is preferable to operate in such a manner that the electrolysis products developing in addition to the tetraethyl lead formed at the anode are also used for the manufacture of fresh complex electrolyte compound, i.e., are regenerated, in order by this method to arrive at an overall reaction which ultimately is based exclusively on lead, hydrogen and olefin as the starting materials. Therefore, in the above-named older processes, regenerating mechanisms have been described by which, on the one hand, the free aluminum compound AlX3 produced as a product of the decomposition of the electrolyte, and on the other hand the alkali metal segregated in the mercury cathode, are used for the regeneration of the alkali metal aluminum complex compound consumed in the electrolysis. In the previous re' generating processes, a portion of the organometallic compounds from the electrolysis cell, namely the free aluminum compound AlX3, entered into the regeneration as such or in their complexly captured form. lt is desirable to the effective performance of the regeneration that the tetraethyl lead be entriely removed from this portion of the organic aluminum compounds subjected to regeneration. This complete purification from tetraethyl lead is not an entirely simple process in actual practice. The process of the invention is not at all encumbered by this diiiiculty. The electrolysis products produced in addition to the tetraethyl lead are naught but the two metals potassium and aluminum which are amalgamated and suspended, respectively, in the mercury. In order for the process to be continuous and economical only these two metallic components must be used in the regeneration of the organic aluminum complex compound. The simultaneous use of organometallic compounds from the electrolyte liquid is eliminated. The electrolysis and the regeneration are, therefore, so to speak, separated from one another by a wall of mercury. The tetraethyl lead is practically entirely insoluble in the mercury. The electrolysis products to be regenerated migrate through this mercury out of the electrolysis cell and can be used directly in the re generation as the purest of starting materials.

The invention accordingly covers a circulatory processA for the manufacture of tetraethyl lead, in which the elec-- trolysis is first performed in the manner described. Thenv the metallic electrolysis products carried out of the cell in the mercury are used at least partially for the production of the complex electrolyte compound KAl(C2H5)4, and then in this form they go back into the electrolysis. This also makes it possible to perform the process in a most simple and economically optimum manner. The couse of these cathodic electrolysis products for the reconstitution of the complex electrolyte compounds can take place according to known processes. It is particularly preferred, within the framework of the circulatory process of the invention, to perform the regeneration so as to incorporate the steps described below.

The accompanying flow sheet depicts a cyclic process according to the invention. ln the flow sheet, production of lead tetraalkyl is represented and the mol proportions of the various streams, except for mercury, is indicated. The cyclic process utilizes a primary electrolysis l, wherein the potassium aluminum tetraalkyl is decomposed and lead tetraalkyl is produced, an exchange reactor 2, wherein potassium aluminum tetraalkyl electrolyte for return to the cell is produced, a displacement reactor 3, wherein the aluminum metal is converted to aluminum trialkyl, a secondary electrolysis cell 4, wherein sodium picked up- -by the mercury in the exchange reactor is separated from the mercury, and a regeneration zone 5, Iwherein sodium, hydrogen, olefin and aluminum trialkylV are utilized to produce sodium aluminum tetraalkyl used in the exchange reactor and displacement reactor.

ln application Ser. No. 114,939, filed lune 5, 1961, abandoned and replaced by Ser. No. 320,607, iiled Oct. 29, i963, now Patent No. 3,285,947, ofthe applicants, it

is told how, by the contacting of potassium amalgam with sodium aluminum tetraalkyl complexes, the corresponding potassium aluminum tetraalkyl complex compound and sodium amalgam could be obtained. It has developed that this exchange reaction is not adversely affected by the aluminum suspended in the potassium amalgam in the framework of the process of the invention. So, in a preferred embodiment of the circulatory process of the invention, the potassium amalgam containing aluminum is first contacted with a quantity of sodium aluminum tetraethyl that is eqiuvalent to the potassium, with the reconstitution of the electrolyte compound lpotassium aluminum tetraethyl and sodium amalgam. The potassium aluminum tetraethyl complex compound thus produced is fed back into the electrolysis cell, thus feeding back to the electrolyte the amount of potassium that was taken from it by the electrolysis.

The aluminum that has been removed, and which is now present in the sodium amalgam in lfinely divided metallic form, is then transformed back into triethyl aluminum in another likewise preferred embodiment of the invention, -by the method of application Ser. No. 217,501, filed Apr. 10, 1962, now Patent No. 3,324,159, wherein the displacement reaction is described. It is taught in this application that metallic aluminum can be transformed with sodium aluminum tetraalkyl compounds in the presence of mercury into free trialkyl aluminum and sodium. This reaction is performed preferably at elevated temperatures, eg., in the temperature range of about 200 C. though the overall range from about 60 to about 250 C. is suitable. According to the invention, the mercury, which in this stage of the process is charged with aluminum and sodium, is made to react with 3 mols of tetraethyl sodium aluminum per mol of aluminum, at elevated temperature, by thorough stirring for example. The restoration reaction thus takes place very rapidly as follows:

The metallic aluminum, therefore, goes back into solution with the formation of triethyl aluminum. This triethyl aluminum can then be transformed back into the sodium aluminum tetraalkyl compound in a simple manner by known processes, such as treatment with sodium hydride and ethylene. This produces 4 moles of tetraethyl sodium aluminum per mol of the aluminum obtained from the electrolysis. 3 mols of this complex compound are used for the transformation of the aluminum into triethyl aluminum as just described, and the remaining mol is used for the previously described exchange reaction of the sodium complex compound with the potassium amalgam to produce the potassium complex compound and sodium amalgam. On the whole, therefore, the reaction equilibrium is thus restored, so that, in view of this continuous regeneration, the ideal condition is fulfilled for the economic production of tetraethyl lead, namely, synthesis from lead, hydrogen and olefin.

It has developed that the displacement reaction between the metallic aluminum in the sodium-charged mercury and the tetraethyl sodium aluminum complex will be best as regards speed and quantity if an electron donor is added in this step in an amount equivalent to the triethyl aluminum that is formed. Suitable donors are, here again, ether or tertiary amines, for example, dialkylethers, such as di-n-butyl ether, or cyclic ethers such as tetrahydrofuran being usable, as well as amines such as triethylamine. The reaction product of this stage of the process will not then be the free triethyl aluminum, but a triethyl aluminum bound to the electron donor, which can be transformed to the complex tetraalkyl compound with alkali hydride and olefin. It may, however, also be preferred according to the invention to separate the electron donor from this complex compound by a distillative treatment, for example. This is possible, for example, by first adding the NaH. According to the teaching of application Ser. No. 45,526, filed July 27, 1960 (Patent 3,255,224, June 7, 1966), the existing complex is then destroyed by the stronger complex former, NaH, and the electron donor can then be separated. The ethylation reaction, however, can also be performed at 200 to 220 C. by passing a current of ethylene at normal pressure through the mixture. yIn this procedure, the danger of the formation of butyl groups by synthesis reaction is slight. In the presence of triethylamine and other easily Volatile donors, the removal of the donor before the addition of ethylene is unnecessary, because when ethylene is passed through the 200 C. reaction mixture, for example, the NEt3 (triethylamine) is distilled away and carried out by the ethylene current -within the first 15 minutes.

The sodium still present in the mercury after the latter has been freed of aluminum can be treated to remove at least part of the sodium and then the amalgam depleted in sodium can be returned to the electrolysis for use as cathode therein. In the treatment of the amalgam, the sodium can be dissolved out in the form of sodium hydroxide in a known manner, such as by treatment with water, but it is also possible, and it is preferred according to the invention, to recover the sodium in the form of metallic sodium by means of a secondary electrolysis after German Patent 1,114,330 and application Ser. No. 27,219, filed May 5, 1960 (abandoned and replaced by Ser. No. 299,689 which matured into Patent 3,234,115, Feb. 8, 1966), and Ser. No. 192,954, filed May 7, 1962 (Patent 3,234,113, Feb. 8, 1966). This metallic sodium can then be used in the regeneration of the tetraethyl sodium aluminum complex from the free triethyl aluminum. This entirely completes the circulatory process.

The advantages of the new process over all previously known processes have already been extensively evaluated. The following is additionally set forth. In contrast to the previous preferred process of the said Ser. No. 129,009, a very much smaller amount of lorganic aluminum complex needs ot be kept in circulation according to the invention. It amounts to approximately 3 to 4 mols of tetraethyl sodium aluminum per mol of tetraethyl lead, i.e., approximately 50-0 to 700 grams of the organic aluminum complex per 327 grams of tetraethyl lead. This represents a considerable simplification over the older process in which the ratio of production to circulating electrolyte amounted to about 1: 10. Very important is the advantage that, both in the electrolysis and in the regeneration, naught but homogeneous organic aluminum compounds are used, not mixtures of various organic aluminum compounds. This considerably simplifies the processing and purification of the compounds in question.

Although the invention has here been explained only with reference to tetraethyl lead, the information also applies accordingly to the manufacture of diethyl mercury, tetraethyl tin and triethyl antimony, and of metal alkyls other than the ethyl derivatives, as is indi cated above.

Example 1 The electrolysis cell is a cylindrical glass vessel with a double jacket and a fiat ground upper edge, which can be sealed tight with a plastic cover. The heating and the removal of the heat produced by the electric currents is performed by means of boiling heptane contained in the double jacket of the glass vessel. Suspended from the cover are two bearings in which a shaft rotates, on which there fastened at 9 mm. intervals four circular copper discs 1 mm. thick and 160 mm. in diameter. The shaft bearing the copper discs is driven from the top through two bevel gears. The bottom halves of the copper discs are immersed in a mercury filled tank made of electrically insulating material (Bakelite, for example) and serve as cathodes during the electrolysis. The tank is also suspended from the cover, in such a manner that a certain amount of space is left at the bottom and at two sides between the tank, and the outer glass vessel in which the heavy electrolysis product can settle during operation.

The copper discs become wetted with mercury. The mercury film picks up the metal separated at the cathode. Due t the rotation of the discs at about 2O rpm., the amalgam is greatly diluted upon immersion in the larger mercury supply in the tank, and thus the mercury ilm is constantly being renewed on the rotating discs. The infeed of fresh mercury into the tank is controlled so that an approximately 0.6% potassium amalgam runs out over an overflow on the tank and can be removed continuously from the cell by a siphon.

Between the copper disc are appropriately cast lead plates about 4 mm. thick, so that, at the beginning of the electrolysis, there will be an electrode spacing between cathode and anode of 2.5 mm. in each case. This spacing is increased by the dissolution of the lead in the course of the electrolysis and runs to a maximum of 4.5 mm. After they are used up, the remnants of the lead plates, which are fastened to appropriately constructed slides, are lifted out with special precautions and are replaced with new plates.

Molten potassium aluminum tetraethyl is poured into the cell as the'electrolyte and electrolyzed at 10G-110 C. with 25() amperes, which requires a voltage of 2.5 volts. The current intensity of 250 amperes corresponds to a current density of 46.5 amperes per square decimeter. With a continuous operation, the following quantities are required per hour: 426 g. KalEt.,e and 15,150 g., i.e., approximately 1.1 liters, of mercury.

The useful weight of each lead plate amounts to about 480-500 grams; 485 g. of lead are dissolved per hour, so that the anodes have to be replaced every 3 hours.

The tetraethyl lead settles in the free Space next to the mercury tank and can be lifted out from time to time. In the upper part of the cell, i.e. especially between the electrodes, there should be substantially nothing but molten electrolyte, although provision can be made by an appropriately adjusted agitation for a certain stirring up of the heavy bottom layer. It can easily be brought about that a portion of the heavy layer of tetraethyl lead, which in itself is only gently stirred, remains coherently on the bottom, while another portion is suspended in droplet form in the electrolyte, in which it is stirred up. This improves the exchange of potassium and aluminum between the amalgam and the primarily separated triethyl aluminum, and renders the tetraethyl lead practically free of triethyl aluminum.

Also continuously removed from the electrolysis cell are 755 grams of tetraethyl lead, which, at 250 amperehours, corresponds to a yield of 100%, and 15.3 kg. of a 0.6% potassium amalgam, which furthermore contains 63 g. of aluminum in suspension. The yield is plentiful, both in regard to potassium and aluminum (91 g. K per hour and 63 g. Al per hour) and in regard to the amount of tetraethyl lead is produced.

The amalgam taken from the electrolysis is then subjected to the exchange reaction with molten NaAlEt4, in a quantity equivalent to the potassium content in the amalgam, at approximately 130 C. preferably in a packed reaction tower in which the reagents are fed in counterow. The size 0f the reaction tower must be such as to assure that the time of stay of the amalgam will be from about seconds to a few minutes. A longer time of stay does no harm, but is uneconomical, because then too great an amount of mercury stands idle in the transposer. The amalgam that then comes out contains sodium and aluminum but not potassium; the molten complex salt is pure KAIEL, and can be fed directly back to the electrolysis.

In connection with a 250-ampere cell, the following quantities are required per hour for the exchange reaction: 390 g. NaAlEt4 and 15.3 kg. 0.6% potassium amalgam; in return, 426 g. KAlEt4 are produced, and 15.3 kg. of an 0.354% sodium amalgam containing in suspension another 63 g. of unmodified aluminum. The quantity of KAlELl corresponds precisely to the amount'consurned in the electrolysis, so that the circulation of electrolyte is a closed cycle.

In a heatable iron kettle filled with inert gas and having a capacity of about 15 litters, the sodium amalgam coming from the exchange tower is reacted at about 200 to 210 C., and with strong agitation, with a mixture of NaAlEt!z and N(C2H5)3 in a molar ratio of 3:4; 1165 grams of NaAlEt4 and 945 grams of N(C2H5)3 are placed in the reactor per hour, preferably being fed continuously. The reactants are lrst let run for 4 hours, and then 15.3 kg. of a 1.4% sodium amalgam and 2.0 kg. of A1Et3-NEt3 can be taken out per hour. The amount of mercury that is tied up in the reactor can be reduced substantially by drawing off the sodium amalgam through an appropriate filter lcandle made of ceramic material or sintered metal, for example. A somewhat greater concentration of aluminum would then remain stationarily in the reactor; this is favorable to the thoroughreaction of the components. On the basis of known industrial principles, it is possible to use expediently a series of several small reactors instead of the single reactor.

The sodium amalgam is extensively freed of its sodium content in a known manner in a secondary electrolysis, in which liquid sodium is obtained at the cathode in an amount of 215 grams of sodium per hour, and is converted to sodium hydride with hydrogen in a known manner. Atthe operating temperatures of 110-120 C. in the secondary cell, the 1.4% sodium amalgam remains perfectly fluid. lf it is desired to remove the sodium from the amalgam with water, the amalgam is best thinned with additional mercury from the circulatory system, before it is put into the decomposer. Equivalent quantities of the Nal-I thus obtained Iand triethyl :aluminum-triethylaminate are briefly stirred together at -90 C., until all the NaH has dissolved. The reaction mixture thus obtained is then placed in a reaction tower which is heated at about 200 C., and is treated with ethylene at about normal pressure. It is best to put the ethylene into the bottom of the high tower filled with the reaction mixlture and to let the ethylene, which is used in excess, bubble through the liquid; the ethylene will carry the triethylamine out with it. After the condensation of the amine, the ethylene carried in the circuit is fed back into the reactor. In this manner, with a reaction time of 6 to 10 hours, tetraethyl sodium aliuminum is recovered, which can be reused in the generation process.

Numerous other electron donors-amines and ethers-- can be used instead of rtriethylamine. The following are here named only by way of example: diethylether, dipropylether, dibutylether, ethylbutylether, tetrahydrofuran, dioxan, tripropylamine, tributylarnine, dimethylamine, dimethylcyclohexylamine, ethylene glycol dialkylether, diand triethylene glycol dialkylether.

The ethylene addition can be performed not only at normal pressure but also with an overpressure of ethylene. Thus, it is possible, for example, to complete the ethylene addition in 2 to 3 hours at i60-170 C. and 5 to 10 atmospheres, or in 1 to 2 hours at higher pressures, or, for example, 30 to 50 atmospheres.

Example 2 The procedure is the same as in Example 1, but plates of tin or Vantimony are used .as anodes. It is possible to then returned to the electrolysis cell. The conditions of the distillation are: .liquid temperature: 100-110 C. at a vacuum of -3 torr, or 140-160 C. at a vacuum of 1-0.1 torr.

In a modification of the process, the electrolyte saturated with metal ethyl can also -be freed of tetraethyl tin or of triethyl antimony in a counterfiow extraction at 80 to 100 C., using an appropriate saturated hydrocarbon such as i-octane, Decalin, paraffin oil etc.

The yields of Sn(C2H5).,= or Sb(C2H5)3 with reference to the throughput are practially quantitative.

Example 3 For the production of diethyl mercury, it is expedient to use the following simple experimental arrangement:

The external vessel is a glass -cylinder with a flat-ground upper edge. The amount of mercury on the bottom of the vessel is divided by the installation of .a cylindrical container of insulating material, such as glass again, into an inner mercury mass of circular cross-section and an outer mercury mass of annular cross-section. The level of the mercury in the inner vessel is expediently as much as several millimeters (1 to 3 mm.) below the margin of the vessel. The inner mercury mass is electrodically insulated from the outer one in this manner, and serves as the anode in the electrolysis. The outer mercury ring serves as a cathode. Just above the surface of the mercury rotates an agitator which continually renews the electrolyte above the surface.

The electrolysis is performed at 110 C. with molten KAlEt4 as the electrolyte. Alt the cathode there forms a mixture of potassium amalgam and aluminum which remains suspended in the amalgam. By the intensive agitation of the electrolyte, it is possible to keep in suspension the diethyl mercury `that is -formed at the anode and separates after the saturation of the electrolyte (approximately 10 g. of HgEt2 dissolve in 100 cc. KAlEt4 at 100 C.) as a second phase of greater specific gravity, so that the covering of fthe mercury electrode with an unbroken stratum of the non-conductive diethyl mercury is prevented. The conditions of the electrolysis are: 5 to 6 volts at an average current density of 35 amperes per square decimeter. From time to time the electrolysis is interrupted, the agitation is stopped, the diethyl mercury is allowed to settle, and is siphoned off lfrom the electrolyte under nitrogen pressure. ln like manner, the supply of anode mercury must be replenished from time to time. At a potassium content of approximately 0.6%, by weight, in the cathode amalgam, the latter is replaced by a mercury that is poorer in potassium or free of potassium.

The yield of reaction products (Al, K and HgEt2) is, with reference to the throughput, quantitative.

While the invention has been described with reference to particular embodiments thereof, these are merely representative, and in no way define the limits of the invention.

The said applications Ser. Nos. 27,220; 129,009; 114,939; and 45,526 are in the names of the applicants herein, Ziegler and Lehmkuhl; Ser. No. 217,501 is in the name of one of us, Lehmkuhl, land one Grimme; and Ser. No. 27,219 and 192,954 are in the names of the applicants herein and said Grimme; and all of these applications are assigned to said Dr. Ziegler.

What is claimed is:

1. Process which comprises passing an electrolysis current between a cathode and an anode through an electrolyte consisting essentially of a complex of the formula KAIR., wherein each R is alkyl, the anode being of a metal Me selected from the group consisting of lead, mercury, tin, and antimony, and the cathode being mercury, the electrolysis comprising decomposition of the electrolyte according to the following equation:

KAlR.-{-mMe- K-i-Al-l-mMeRn wherein R and Me are as is defined above, n is the valence 10 of Me and the product of m and n is 4, the metal alkyl 4being produced at the anode and the potassium being produced at the cathode and forming an amalgam With the mercury, the aluminum metal bein-g in the amalgam, and separating aluminum from the amalgam.

2. Process according to claim 1, wherein each R contains 2-6 carbon atoms.

3. Process according to claim 2, wherein Me is lead.

4. Process according to claim 3, wherein each IR is ethyl.

S. Process according to claim 1, wherein the electrolyte is moved relative to the cathode to increase contact between anodic reaction products and the cathode. 6. Process according to claim 1, wherein metal alkyl and aluminum-containing potassium amalgam are removed from the cell, and potassium aluminum tetraalkyl is added to the cell, and consumption of potassium aluminum tetraalkyl in the cell is substantially quantitatively according to said equation.

7. Process according to claim 6, wherein the electrolysis is continuous, the electrolysis being carried out during metal alkyl and amalgam removal and during addition of potassium aluminum tetraalkyl.

8. Process according to claim 2, wherein the electrolyte is moved relative to the cathode to increase contact between anodic reaction products and the cathode.

9. Process according to claim 2, wherein metal alkyl and aluminum-containing potassium amalgam are removed from the cell, and potassium aluminum tetraalkyl is added to the cell, and consumption of potasium aluminum tetraalkyl in the cell is substantially quantitatively according to said equation.

10. Process according to claim 9, wherein the electrolysis is continuous, the electrolysis being carried out during metal alkyl and amalgam removal and during addition of potassium aluminum tetraalkyl.

11. Process for an electrolysis according to claim 1, wherein:

(a) potassium amalgam produced in said electrolysis is subjected to an exchange reaction wherein it is contacted with sodium aluminum tetraalkyl for formation of a sodium amalgam and potassium aluminum tetraalkyl,

(b) potassium aluminum tetraalkyl produced in the exchange reaction is used as eelctrolyte in said electrolysis,

(c) aluminum metal produced by the electrolysis is separated from the amalgam by subjecting it to a displacement reaction wherein it is contacted with sodium aluminum tetraalkyl in the presence of mercury for the following reaction:

wherein R is as defined hereinbefore and sodium produced forms an amalgam with mercury present, and

(d) sodium amalgam produced inthe process is treated to remove at least part of the sodium thereof and is then returned to the electrolysis for use as cathode therein.

12. Process according to claim 11, wherein the potassium amalgam subjected to the exchange reaction contains aluminum produced in the electrolysis and the sodium amalgam produced in the exchange reaction is an al-uminumcontaining sodium amalgam, and the aluminum-containing sodium amalgam is subjected t0 the displacement reaction, and the sodium amalgam from the displacement reaction is treated for removal of sodium to provide mercury for return to the electrolytic cell and use therein as cathode.

13. Process according to claim 12, wherein R contains 2-6 carbon atoms.

14. Process according to claim 13, wherein aluminum trialkyl formed in the displacement reaction is converted 11 to sodium aluminum tetraalkyl, and the sodium aluminum tctraalkyl so produced is Vused for requirement of the cyclic process.

15. --Process according to claim 14, wherein the sodium aluminum tetraalkyl produced from the aluminum trialkyl is used for the requirements of sodium aluminum tetraalkyl in the exchange reaction and in the displacement reaction.

16. Process according to claim 14, wherein sodium removed from sodium amalgam is utilized for production of sodium aluminum tetraalkyl from said aluminum trialkyl.

17. Process according to claim 14, wherein the displacement reaction is carried out in the presence of an electron donor, and production of sodium aluminum tetraalkyl from aluminum trialkyl is by reactionof aluminum trialkyl, sodium hydride, and ethylene, and the 12 electron donor is' separated after reaction of sodium hydride with aluminum trialkyl.

18. Process according to claim 14, wherein each R is ethyl.

19. Process according to claim 18, wherein Me is lead. 20. Process according to claim 14, wherein the displacement reaction is carried out in the presence of an electron donor.

21. Process according to claim 20, the electron donor being selected from the group consisting of ethers and amines.

References Cited UNITED STATES PATENTS 3,164,538 1/1965 Ziegler et al. 204-59 HONARD S. WILLIAMS, Primary Examiner.

JOHN MACK, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,372,097 March 5, 1968 Karl Ziegler et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading to the printed specification, after line 7, insert Claims priority, application Germany, July 2, 1962, 29495 Signed and sealed this 7th day of April 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, JR.

Commissioner of Patents Edward M. Fletcher, Jr.

Attesting Officer 

1. PROCESS WHICH COMPRISES PASSING AN ELECTROLYSIS CURRENT BETWEEN A CATHODE AND AN ANODE THROUGH AN ELECTROLYTE CONSISTING ESSENTIALLY OF A COMPLEX OF FORMULA KAIR4 WHEREIN EACH R IS ALKYL, THE ANODE BEING OF A METAL ME SELECTED FROM THE GROUP CONSISTING OF LEAD, MERCURY, TIN, AND ANTIMONY, AND THE CATHOD BEING MERCURY, THE ELECTROLYSIS COMPRISING DECOMPOSITON OF THE ELECTROLYTE ACCORDING TO THE FOLLOWING EQUATION: 